Bax is a 20-22 kDa member of the Bcl-2 family of proteins involved in regulation of programmed cell death, or apoptosis. In murine thymocytes, it is expressed primarily as a cytoplasmic protein. Over-expression of Bax promotes apoptosis by formation of homodimers and through heterodimerization with Bcl-2, an inhibitor of apoptosis. The monoclonal antibody 2D2 reacts with an N-terminal epitope between amino acids 3-16 of human Bax. It can bind both soluble and detergent-altered forms of Bax as well as Bax-Bcl-2 and Bax-Bcl-xL heterodimers.